The present invention relates to a projection exposure method and a projection exposure apparatus for projecting and exposing a predetermined pattern onto a substrate mounted on a substrate stage via a projection optical system. More specifically, the present invention relates to a projection exposure method and a projection exposure apparatus, which measures a mark formed by exposure in a plurality of shot areas on the substrate, to thereby obtain position information of each shot area by statistical processing.
This application is based on Japanese Patent Application No. 2000-140979, the contents of which are incorporated herein by reference.
Heretofore, projection exposure apparatus have been used when manufacturing semiconductor devices or liquid crystal display devices by a photolithography process, which projects a pattern image of a photo mask or a reticle (hereinafter generally referred to as a xe2x80x9creticlexe2x80x9d) onto each shot area on a photosensitive substrate via a projection optical system. Recently, as such kind of projection exposure apparatus, a so-called step and repeat type exposure apparatus, for example, a reduction projection type exposure apparatus (stepper) has been used in many cases. In this apparatus, a photosensitive substrate is mounted on a two-dimensionally movable stage and the substrate is moved step by step by this stage, to thereby repeat an operation for sequentially exposing a pattern image of the reticle onto each shot area on the photosensitive substrate.
For example, micro devices such as semiconductor devices are formed by overlapping a circuit pattern having multiple layers, on a wafer coated with a photosensitive material, as a photosensitive substrate. Hence, at the time of projection exposure of the circuit pattern in the second or further layers onto the wafer, it is necessary to perform positioning of each shot area on the wafer having a circuit pattern already formed thereon, with a pattern image of a reticle to be exposed next, that is, to perform accurate positioning (alignment) between the wafer and the reticle.
For example, with respect to one wafer having a shot area, on which a circuit pattern is to be exposed, arranged thereon in a matrix, as a method for aligning the wafer at the time of performing overlap exposure, so-called enhanced global alignment (EGA) disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. Sho 61-44429 has become predominant.
The EGA method is a positioning method as described below. That is, at least three areas (hereinafter referred to as xe2x80x9cEGA shotxe2x80x9d) of a plurality of shot areas formed on the wafer are specified, and the coordinate position of the alignment mark (mark) annexed to each shot area is measured with, for example, an off-axis alignment system. Thereafter, error parameters (offset, scale, rotation and perpendicularity) related to the array characteristics (position information) of the shot area on the wafer are determined based on the measurement and design values, by statistical operation involving the method of least squares. Based on the determined parameter values, the coordinate value for the design is then corrected with respect to all the shot areas on the wafer, and the wafer stage is moved step by step, using a baseline quantity, being a distance between the projection optical system and the off-axis alignment system, in accordance with this corrected coordinate value. As a result, the projected image of the reticle pattern and the plurality of shot areas on the wafer are precisely overlapped and exposed at a working point (a reference point at which the coordinate value is measured or calculated, for example the center of the shot area) set in the shot area.
However, the above described conventional projection exposure method and projection exposure apparatus have problems described below.
In the case where the wafer scaling (scaling of the whole wafer) and shot scaling (scaling for each shot area) of the above error parameters are calculated with the EGA measurement, the shot size on the wafer and the shot size at the time of exposure are controlled so as to coincide with each other, by driving optical lenses in the projection optical system to adjust the projection magnification (hereinafter referred to as xe2x80x9clens magnification drivexe2x80x9d), as shown in a flowchart in FIG. 9. In this case, however, it is found that by performing lens magnification drive, mechanical deviation occurs between lenses in the projection optical system, thereby slightly shifting the optical axis of the projection optical system.
Since positioning of the wafer has been heretofore performed based on the results of EGA performed before the deviation occurs, without taking this deviation of the optical axis into consideration, the pattern image is exposed in a state of being shifted, causing a problem in that the relative position of each shot area formed on the wafer in which the circuit pattern has been already formed and the pattern image of the reticle to, be exposed next is shifted, that is, the overlapping accuracy decreases.
In order to avoid this problem, there has been adopted a method in which evaluation exposure is performed beforehand under predetermined conditions, and the error parameters obtained by the above described EGA measurement are corrected using the evaluation results. However, due reasons such as, hysteresis exists in the lens magnification drive, or conditions at the time of evaluation, such as atmospheric pressure or the like are different at the time of actual exposure, the deviation of the optical axis which actually occurs does not always coincide with the evaluation result, thus leaving a problem in that deterioration of the overlapping accuracy cannot be solved.
The present invention has been completed in view of the above situation, with an object of providing a projection exposure method and a projection exposure apparatus which can prevent deterioration of the overlapping accuracy, even if the optical axis is shifted with the adjustment of the projection magnification of the projection optical system.
In order to achieve the above object, the present invention adopts the following constructions corresponding to FIG. 1 to FIG. 7 showing embodiments of the present invention.
The projection exposure method of the present invention is characterized in that in a projection exposure method in which after imaging characteristics of a projection optical system (9) are adjusted based on measurement results of marks (YEM, XEM) formed on a substrate (W) mounted on a substrate stage (10), the substrate (W) is exposed by a predetermined pattern via the projection optical system (9), information related to an imaging position of the projection optical system (9) is determined after adjustment of the imaging characteristics and before the exposure of the substrate (W).
In this projection exposure method, since the information related to the imaging position of the projection optical system is determined after adjustment of the imaging characteristics and before exposure of the substrate, positioning error of the substrate attributable to the deviation of the optical axis can be eliminated. As a result, it becomes possible to expose the pattern on the substrate with predetermined accuracy, and hence deterioration in the overlapping accuracy can be prevented beforehand.
If the deviation of the optical axis is measured during the actual exposure processing step, the evaluation result does not differ from the actual exposure, as in the case where the evaluation exposure is performed separately. As a result, there is the effect that the image shift quantity can be obtained accurately and quickly.
In an other embodiment, the projection exposure method is a procedure wherein the imaging characteristics include projection magnification of the projection optical system, and by measuring information related to the imaging position of the projection optical system after adjustment of the imaging characteristics and before exposure of the substrate, information related to the imaging position of the projection optical system is obtained.
In an other embodiment, the projection exposure method is a procedure wherein information related to the imaging position is measured by measuring position information of a mark on the substrate stage via the projection optical system.
As a result, with this projection exposure method, an effect can be obtained where the deviation amount of the optical axis can be detected more accurately.
In an other embodiment, the projection exposure method is a procedure wherein position information of either a reference mark set on the substrate stage or a mark on the substrate mounted on the substrate stage is measured via the projection optical system.
As a result, with this projection exposure method, an effect can be obtained where the deviation amount of the optical axis can be detected accurately, using either the reference mark or the mark on the substrate.
The projection exposure method according to a fifth aspect is a procedure for measuring the position information of the mark on the substrate stage via a mask having the predetermined pattern formed thereon.
As a result, with this projection exposure method, an effect can be obtained where the deviation amount of the optical axis, designating the mask as a reference, can be detected, thereby improving the alignment accuracy with respect to the mask.
In an other embodiment, the projection exposure method is a procedure wherein information related to the imaging position is measured by measuring a relative position of a mask mark on the mask and a mark on the substrate stage.
As a result, with this projection exposure method, an effect can be obtained where the deviation amount of the optical axis, designating the mask as a reference, can be detected with the mask mark and the mark on the substrate stage.
In an other embodiment, the projection exposure method is a procedure wherein adjustment of projection magnification is performed based on the measurement result obtained by measuring the position information of the mark on the substrate with predetermined measurement accuracy.
As a result, with this projection exposure method, an effect can be obtained where measurement can be executed in a state closer to the actual exposure light, at the time of measuring the mark on the substrate.
In an other embodiment, the projection exposure method is a procedure wherein position information of a plurality of shot areas on the substrate is calculated, based on the measurement results of the plurality of marks with higher measurement accuracy than the predetermined measurement accuracy.
As a result, with this projection exposure method, an effect can be obtained where error parameters can be obtained by performing measurement in a state closer to the actual exposure light, thereby enabling improvement in the overlapping accuracy. Another effect can be obtained where even if an error occurs in the projection magnification adjustment, this can be quickly detected at the time of measurement with higher measurement accuracy than predetermined measurement accuracy, thereby enabling prevention of poor exposure beforehand.
In an other embodiment, the projection exposure method is a procedure wherein readjustment of the projection magnification is performed, based on the measurement results of the plurality of marks with higher measurement accuracy than the predetermined measurement accuracy, and the calculated position information of a plurality of shot areas on the substrate is corrected, based on the information related to the imaging position respectively measured before and after the readjustment.
As a result, with this projection exposure method, an effect can be obtained where even if deviation of the optical axis occurs with the readjustment of the projection magnification, the error parameters can be reliably corrected, thereby maintaining the overlapping accuracy.
In an other embodiment, the projection exposure method is a procedure wherein it is determined whether measurement of information related to the imaging position is to be performed or not, depending on the readjustment amount of the calculated projection magnification.
As a result, with this projection exposure method, unnecessary sequences are not performed, thereby enabling improvement in the throughput in the exposure processing.
In an other embodiment, the projection exposure method is a procedure wherein position information of a plurality of shot areas on the substrate and the adjusted amount of the projection magnification are calculated, by performing statistical processing using the results of measurement of position information of a plurality of marks, and the calculated position information of the plurality of shot areas on the substrate is corrected based on the information related to the imaging position respectively measured before and after the adjustment of the projection magnification.
As a result, with this projection exposure method, positioning error of the substrate attributable to the deviation of the optical axis can be eliminated, and hence a pattern can be exposed with predetermined accuracy on a shot area on the substrate, thereby enabling prevention beforehand of deterioration in overlapping accuracy. Since the deviation of the optical axis is measured during the actual exposure processing step, the evaluation result does not differ from the actual exposure, as in the case where the evaluation exposure is performed separately. Hence, there is the effect that the image shift quantity can be obtained accurately and quickly.
In an other embodiment, the projection exposure method is a procedure wherein it is judged whether measurement of information related to the imaging position is to be performed or not, depending on the adjusted volume of the projection magnification calculated by the statistical processing.
As a result, with this projection exposure method, unnecessary sequences are not performed, thereby enabling improvement in the throughput in the exposure processing.
In an other embodiment, the projection exposure method is a procedure wherein the position information of a plurality of marks is measured with or without the projection optical system.
As a result, with this projection exposure method, even if marks on the substrate are measured using either an alignment sensor of the TTR (or TTL) type or the off-axis type, there can be obtained an effect where positioning error of the substrate attributable to the deviation of the optical axis can be eliminated.
Moreover, the present invention provides a device manufacturing method involving a step for transferring a device pattern formed on a mask onto a substrate, using the projection exposure method according to either of the above described methods.
A projection exposure apparatus of the present invention is a projection exposure apparatus (1) for projection-exposing a predetermined pattern formed on a mask (R) onto a substrate (W) mounted on a substrate stage (10) via a projection optical system (9), comprising: a measurement device (16, 17) which measures position information of a plurality of marks (YEM, XEM) formed on the substrate (W); an adjustment device (22) which adjusts the imaging characteristic of the projection optical system (9) based on the results of measurement by the measurement device (16, 17), and a detection device (19) which obtains information related to a change of the imaging position of the projection optical system (9) attributable to adjustment of the imaging characteristic by the adjustment device (22).
Therefore, according to the projection exposure method and the projection exposure apparatus of the present invention, by adjusting the imaging characteristics of the projection optical system (9), based on the error parameters calculated by the EGA measurement, being the measurement results for the marks (YEM, SEM), even if a deviation of the optical axis occurs, the above described error parameters can be recorrected, using the information related to the change of the imaging position of the projection optical system (9) after adjustment of the imaging characteristics. Therefore, the error parameters include the deviation of the optical axis resulting from adjustment of the imaging characteristics. Hence, a predetermined pattern can be exposed on the substrate (W) with predetermined positioning accuracy being maintained.
As a result, with this projection exposure apparatus, positioning error of the substrate attributable to the deviation of the optical axis can be eliminated. Hence, it becomes possible to expose a pattern on the substrate with predetermined accuracy, and deterioration in the overlapping accuracy can be prevented beforehand.
If the deviation of the optical axis is measured during the actual exposure processing step, the evaluation result does not differ from the actual exposure, as in the case where the evaluation exposure is performed separately. As a result, there is the effect that the image shift quantity can be obtained accurately and quickly.
In an other embodiment, the projection exposure apparatus has a construction where the imaging characteristics include projection magnification of the projection optical system, and the detection device respectively detects the information related to the imaging position of the projection optical system before and after adjustment by the adjustment device.
In an other embodiment, the projection exposure apparatus has a construction where the detection device measures the position information of a reference mark placed on the stage, or a mark on the substrate, via the projection optical system.
As a result, with this projection exposure apparatus, an effect can be obtained where the deviation amount of the optical axis can be detected more accurately, by using either of the reference mark or the mark on the substrate.
In an other embodiment, the projection exposure apparatus has a construction where the calculation device performs statistical processing using the results of measurement results by the measurement device, and calculates the position information of a plurality of shot areas on the substrate and the adjusted amount by the adjustment device, and the correction device corrects the position information of the plurality of shot areas on the substrate calculated by the calculation device, based on information related to the imaging position detected by the detection device.
As a result, with this projection exposure apparatus, error parameters can be obtained by performing measurement in a state closer to the actual exposure light, thereby enabling improvement in the overlapping accuracy. There is also obtained an effect where even if an error occurs in the projection magnification adjustment, this can be quickly detected at the time of measurement with higher measurement accuracy than predetermined measurement accuracy, thereby enabling prevention of poor exposure beforehand.
In an other embodiment, the projection exposure apparatus has a construction where the measurement device measures the position information of the marks by either one of a first measuring method for measuring the position information via the projection optical system, and a second measuring method for measuring the position information without using the projection optical system.
As a result, with this projection exposure apparatus, even if marks on the substrate are measured using either alignment sensor of the TTR (or TTL) type or the off-axis type, there can be obtained an effect that positioning error of the substrate attributable to the deviation of the optical axis can be eliminated.